Subsurface fluid drainage and storage systems

Abstract

There is provided by the invention a subsurface drainage system which promotes efficient and controlled subsurface drainage of fluids, such as irrigation water, applied to the surface of land such as a football field. A drain core apparatus is provided that provides rapid infiltration and later movement of subsurface fluids, but which is resistant to settling, compacting and crushing. The drain core is a thermoplastic mat having crush-resistant support members integrated with and upon a backing grid which holds the support members in spaced relation to one another. Fluid flowing into and through the drain core is collected and stored in a fluid storage container. The fluid storage container is adapted to be buried beneath the ground, and has an easily assembled internal support structure composed of vertically layered thermoplastic mats. The mats permit fluids to flow freely within the container, and yet lend vertical and structural stability to the container. Subsurface fluids gathered by the system may be re-applied to the surface to conserve water, fertilizer, and the like, to minimize evaporation, and to minimize water pollution.

I claim: 
     
       1. A system for directing fluid drainage from a land surface and collecting said fluid drainage below said surface, said system comprising: a subbase beneath said surface, said subbase having at least one sloped surface;   a drainage collection point located at the bottom of said at least one sloped surface;   a drain core overlying said subbase, said core including a mat comprising: a laterally extensive backing grid having a plurality of intersecting struts defining grid openings therebetween; and   a plurality of spaced support members projecting from said backing grid, whereby fluid may flow through said backing grid and between said support members;     a fluid collector disposed at said drainage collection point; and   a subsurface container in fluid communication with said fluid collector to store fluids which drain from the surface into the fluid collector past the drain core, wherein said subsurface container comprises: a flexible, substantially impermeable envelope enclosing a fluid reservoir, said envelope including a port to permit fluid communication with an interior of said subsurface container; and   a plurality of drainage mats stacked adjacent one another within said fluid reservoir to support said envelope, each drainage mat comprising a backing grid having a plurality of intersecting struts defining grid openings therebetween, and a plurality of spaced support members projecting from said backing grid to allow fluid to pass between said plurality of drainage mats.     
     
     
       2. The system of claim 1, further comprising an impermeable liner disposed between said subbase and said drain core. 
     
     
       3. The system of claim 1, further comprising a semipermeable geotextile fabric disposed between said subbase and said drain core. 
     
     
       4. The system of claim 1, further comprising a semipermeable geotextile fabric disposed in flush contact above said drain core. 
     
     
       5. The system of claim 1, wherein said fluid connector comprises a perforated collector pipe connected at one end to said port of the envelope. 
     
     
       6. The system of claim 1, wherein each of said support members of said drain core mat comprises a tubular member extending substantially perpendicularly from said backing grid, and each tubular member defines a central longitudinal axis extending through an intersection of said struts forming said grid to allow fluid flow through an interior of said tubular member. 
     
     
       7. The system of claim 6, wherein said tubular support members are substantially cylindrical. 
     
     
       8. The system of claim 7, wherein said support members are disposed upon said backing grid in a uniform rectangular array defined by a plurality of substantially perpendicular rows and columns. 
     
     
       9. The system of claim 5, wherein: said plurality of drainage mats are stacked vertically within said fluid reservoir.   
     
     
       10. The system of claim 9, wherein: each of the support members of said drainage mats comprise a tubular member extending substantially perpendicular from said backing grid and each tubular member defines a central longitudinal axis extending through an intersection of said struts forming said grid;   the tubular support members of adjacent drainage mats are aligned with one another in the vertical direction so that the central longitudinal axes of vertically adjacent tubular support member are substantially aligned along a common axis; and wherein said system further comprises:   an elongated clip for insertion between at least two vertically adjacent aligned tubular support members to maintain the substantial vertical alignment of the tubular support members of adjacent drainage mats.   
     
     
       11. The system of claim 1, further comprising a pump in fluid communication with said container, whereby fluid within the container may be pumped to the surface. 
     
     
       12. The system of claim 1, further comprising a sensor adapted to monitor characteristics of the fluid at a selected point in the system. 
     
     
       13. The system of claim 10, wherein said tubular support members are substantially cylindrical. 
     
     
       14. The system of claim 10, wherein said elongated clip includes at least one flange for contacting at least one strut on each of at least two vertically adjacent drainage mats. 
     
     
       15. The system of claim 14, wherein said elongated clip includes two flanges for contacting two intersecting struts on each of at least two vertically adjacent drainage mats. 
     
     
       16. The system of claim 1, wherein said drain core is substantially formed from a thermoplastic material. 
     
     
       17. The system of claim 16, wherein said plurality of drainage mats are substantially formed from a thermoplastic material. 
     
     
       18. A system for directing fluid drainage from a substantially vertical structure extending beneath a land surface, said substantially vertical structure having an exterior surface which faces a subbase beneath the surface, said system comprising: a drainage collection point located within the subbase adjacent a bottom end of said substantially vertical structure;   a drain core positioned between said exterior surface and said subbase, said drain core including a mat comprising:   a laterally extensive backing grid having a plurality of intersecting struts defining grid openings therebetween; and   a plurality of spaced support members projecting from said backing grid, whereby drainage fluid may flow through said backing grid and between said support members; and   a fluid collector disposed at said drainage collection point for collecting said drainage fluid and directing said drainage fluid away from the exterior surface.   
     
     
       19. The system of claim 18, further comprising an impermeable liner disposed between said exterior surface and said drain core. 
     
     
       20. The system of claim 18, further comprising a semipermeable geotextile fabric disposed between said drain core and said subbase. 
     
     
       21. The system of claim 18, wherein said substantially vertical structure comprises a foundation wall of a building. 
     
     
       22. The system of claim 18, further comprising: a subsurface container in fluid communication with said fluid collector to store fluids which drain from the surface into the fluid collector.   
     
     
       23. The system of claim 22, wherein said subsurface container comprises: a flexible, substantially impermeable envelope enclosing a fluid reservoir, said envelope including a port to permit fluid communication with an interior of said subsurface container; and   a plurality of drainage mats stacked adjacent one another within said fluid reservoir to support said envelope, each drainage mat comprising a backing grid having a plurality of intersecting struts defining grid openings therebetween, and a plurality of spaced support members projecting from said backing grid to allow fluid to pass between said plurality of drainage mats.   
     
     
       24. The system of claim 22, further comprising a pump in fluid communication with said container, whereby fluid within the container may be pumped to the surface. 
     
     
       25. The system of claim 24, further comprising a sensor adapted to monitor characteristics of the fluid at a selected point in the system.